Concrete is the second most used material in the world after water and recent trends show no slowing down of the concrete use around the world. Concrete is also a huge contributor to CO2 emissions as it makes up 8% of emissions. This study investigates the optimization of concrete structures to reduce environmental impact while maintaining structural integrity and cost-effectiveness, e.g. how to make a concrete structure more sustainable. A previous report where quay wall designs of different materials were compared in regard to the CO2-emissions and life cycle assessment found that a concrete quay wall had 43% more emissions than a steel quay wall. The goal of this study is to reduce the overall CO2 equivalent emissions related to a concrete structure by 50% and make the design more sustainable.
A concrete ship lock chamber as part of the Delta21 project is used as a case study. To measure the positive effect of sustainability two chambers are designed; a base case chamber designed based on what is most commonly done in practice in the structural engineering field, and an alternative chamber design with the aim of making the concrete lock chamber more sustainable. A partial life cycle assessment (LCA) is performed on both of the two design alternatives. The optimization of the alternative chamber design focused on minimizing global warming potential (GWP) by adjusting the reinforcement-to-concrete ratio and incorporating structural elements such as plated steel anchors. The two alternatives are analysed comparably as they are designed under the exact same conditions, in the same environment and with the same functionality aspects.
The base case structure is a U-basin concrete chamber with tapered walls. The alternative optimised structure enhances the structural behaviour of the chamber wall by adding anchors. This reduces the moments by 88% and the shear force by 56% compared to the base case design. By changing the structural wall type in the chamber by adding anchors, the concrete volume could be reduced by 47% between the base case design and the optimised design. This also allows for a reduction of concrete strength class, reinforcement volume, underwater concrete floor thickness and the number of tension piles for the construction pit. The LCA reveals a 55% reduction in the GWP for the alternative concrete chamber design, compared to the base case design. An optimum reinforcement ratio for the alternative concrete chamber anchored wall of 2.3% is identified, resulting in a balance between structural performance and environmental sustainability without increasing material costs. This ratio doesn’t incorporate labour cost which might affect this optimum ratio by lowering it. This demonstrates the potential for achieving environmentally responsible solutions without compromising the structural integrity of a structure or incurring additional costs.
The study highlights the potential for integrating sustainability objectives into concrete structure design, with recommendations for further research including exploring alternative materials and advanced optimization techniques.

The offshore renewable energy market is rapidly growing, particularly in wind and solar sectors. The intermittent nature of these energy sources underscores the necessity for offshore energy storage solutions. Among the techniques being explored, Marine Pumped Hydro-Energy Storage (MPHES) emerges as a promising option. This innovative concept operates similarly to artificial lakes, where water is stored and released to generate electricity. In the MPHES system, a seabed-based reservoir is established, in which water flows, driving turbines to generate electricity. During periods of energy surplus, the system is charged by pumping water out of the reservoir...

This master thesis investigates the influence of flanges on the shear capacity of reinforced non-rectangular members without shear reinforcement. The study adapts the evaluation procedure developed by Yang (2014) for rectangular cross-sections to analyze plates with holes, I-beams and T-beams.

Bent up bars were prescribed as shear reinforcement in the first half of the twentieth century, stirrups after the 1960’s. In current Eurocode, bent up bars can be applied again, but restrictions with respect to the maximum shear strength should be followed. Goal of this report is to provide background for this shear strength restriction and provide an assessment method for concrete structures reinforced with bent up bars.

First part of the report analyses critical design aspects of bent up bars in the transfer of shear stresses with help of truss models. Second part explores the shear strengths of reinforcement sections and concrete struts with help of outcomes of experiments performed in the past. In last part, the obtained insights are collected and captured into a conceptual model. This model is employed to describe the expected failure mechanism of bent up bars and reflect on assessment methods and maximum shear strengths of specimen reinforced with bent up bars.

Consequence of the application of bent up bars in concrete structures is the formation of cracks in the supporting concrete strut by curved sections of bent up bars. The remaining shear strength of concrete structures depends on the shear resistance of cracked concrete struts.

The findings in this report implies that any model based on the tensile strength of inclined members is applicable for the analysis of bent up bars as long as the applied shear stresses are limited to ten percent of the compressive strength. Also, the application and assessment of bent up bars in concrete structures requires special attention to: shear and flexural reinforcement inclusive designs, cover spalling mechanisms, and detailing of anchorage regions flexural reinforcement bars.

The growing demand for renewable energy sources has led to the deployment of wind turbines worldwide. One of the most critical parts of the wind turbine is the foundation which plays an important role in maintaining the structural integrity and reliability of the towers throughout the service life. This research project is a case study that focuses on validating the numerical model against the experimental values from an operational onshore wind turbine foundation present at Riemst, Belgium while considering the effect of hydration heat during the concrete curing process. The main aim of this research is to study and compare the behavior of the steel stresses in the on-site foundation with that of the numerical analysis and to see whether an adequate match can be obtained. The study begins with the development of a three-dimensional symmetrical finite element model that captures its intricate geometrical and material properties. The structure’s behavior is simulated under realistic loading conditions to assess its structural performance and identify potential areas of concern. To validate the accuracy of numerical analysis, experimental data obtained from fiber optic sensors are used. After converting the measured strains into stresses, they are carefully compared with the finite element analysis results to identify any variations and fine-tune the model. The validation of the FE model is performed using a 2D plate model in SCIA engineering. The research investigates the effects of hydration heat along with the structural analysis in FEA on the stresses experienced by the steel elements in the mass structure. This further extends to the effects of bedding and inclined piles combined with the thermo-mechanical analysis where properties such as stiffness are varied in the simulations to study their influence on the structural response. It is imperative to note that utilizing the FE model with solely non-linear structural analysis can lead to a significant overestimation of the expected field results, up to a whopping 87 times. To mitigate this issue, the variant with thermo-mechanical analysis is implemented, reducing this estimation to a maximum factor of 58 compared to the field data. It is crucial to achieve a satisfactory level of the project through iterative modifications. Implementing soil bedding on all sides in the thermo-mechanical model is one such step to effectively reduce steel stress to an acceptable level. The model showed steel stresses that are approximately 26 times higher than the actual experimental values. Along with reducing the steel stresses, the crack widths have decreased considerably from 3.4mm to 2.35mm. Hence, the effective way to perform the numerical simulation is to consider thermal-mechanical coupling along with minimizing assumptions and ensuring sufficient stiffness to the structure for reliable assessments of steel stresses and structural integrity of onshore wind turbine foundations. The findings contribute valuable insights into the foundation’s structural behavior under varying operational conditions, highlighting areas of strength and potential advancement. Moreover, the outcomes from this investigation can assist engineers and designers in making informed decisions during the planning and construction phases of wind turbine foundations, leading to more cost-effective and robust structures. Additionally, the methodologies present here may serve as a framework for future research in this field.

Across the Netherlands close to 70 prestressed concrete T-beam bridges with cast-in-between slabs and transverse prestressing built in the 60's and are still in service. The current code NEN-EN 1992-1-1+C2:2011 assesses the shear capacity more conservatively. In addition, the NEN-EN 1991-2+C1:2015 prescribes an increased traffic load. This results in this type of bridge not complying with the current codes and the shear capacities are considered insufficient. However, upon inspection these bridges do not show signs of distress. This suggests the presence of additional load-carrying capacity, which is not considered in the current Eurocode.

Non-linear finite element analysis (NLFEA) can be used to accurately approximate the structural behaviour. This includes yielding of steel, cracking and crushing of concrete, the development of alternative load paths as well as snap-back and snap-through behaviour. However, performing each load step requires a great amount of computational effort depending on the amount of degrees of freedom of the model. In FEA a continuous shape is divided into discrete elements which together form a mesh. These meshes can be volumes, surfaces or lines.

To describe the geometry of the prestressed concrete T-beam bridges with cast-in-between slabs either volume elements or multiple surface meshes in different planes are required. Using a mesh of solids would result in system with such a high number of degrees of freedom which might even exceed the available computational capabilities or result in a very long duration of the analysis at best. Using shell elements to construct the mesh reduces the number of degrees of freedom by at least two thirds.

In this thesis I investigate to which extent we can simulate the structural behaviour of a prestressed T-beam slab bridge deck using a non-linear finite element model with a 3D non-planar mesh of shell elements. The Vechtbrug bridge near Muiden was a bridge of this type. A team of researchers from TU Delft have performed several collapse tests on this bridge. This includes extensive measurements of all the experiments as well as material testing on concrete and steel samples. For my own research, a single case study is conducted by recreating collapse tests performed on the Vechtbrug in which both isolated beams and unmodified spans have been loaded past failure. The results of the material tests provide accurate material properties as input for my numerical models. The results of the collapse tests allow for verification and validation of the outcome of the performed finite element analyses.\\

The results of the numerical analyses show a close approximation of the true collapse load with an overestimation of 15\% for the isolated beam model and 12\% for the cooperative beams model. The deflection again is overestimated with 18 and 56\%. The deflection of the adjacent beams relative to the loaded beam is too low. The numerical model is underestimating the transverse load distribution by $\pm$ 25\% for the adjacent beams and $\pm$ 34\% for the beams adjacent to those. The Guyon Massonnet method was applied to estimate the transverse load distribution with the supplied material properties and including the two cross beams. By contrast, the results were an overestimation of approximately 70% for the immediate adjacent beams. In the third numerical analysis the complete bridge deck and ultimate limit state verification is performed by applying the prescribed traffic load with all safety factors applied. The bridge can withstand 234\% of the prescribed load which agrees with the lack of damage present on the Vechtbrug after experiencing over 50 years of traffic load.

The results show that a non-planar shell mesh can generate a realistic structural response considering the collapse load approximates the actual one found in the collapse tests. However, this is somewhat limited for decks consisting of multiple beams since the implementation of the transverse load distribution in the numerical model was inaccurate. The structural response of the structure was too ductile in the numerical analysis with the deflection being overestimated and the strain under the loading plate double the value of the collapse test. Both Mustafa and Ensink have performed a numerical analysis of the isolated beam model using a mesh of solid elements prior to my thesis work. The results of the isolated beam model match closely in both the results of the NLFEA performed by Mustafa and Ensink. The solid mesh does yield more realistic cracking patterns. The isolated beam model showed the required evidence to demonstrate the activation of arching action: An increase in the horizontal reaction force required to lateral restrain the beam with the bending crack occurring under the loading plate so the arch action phenomenon could be activated. In the complete deck model evidence of compressive membrane action in the transverse direction was detected. In both the complete deck models, evidence of lateral confinement was demonstrated, increasing the maximum compressive stress of the concrete.

Finally we can conclude that a NLFEA with a 3D non-planar mesh of shell elements yields accurate results when considering a single strip of the bridge deck. However, the model with a the mesh representing the complete bridge deck, the capacity of the transverse load distribution is underestimated and the structure shows overly ductile behaviour. The model is capable of including the load-carrying mechanisms arch-action, compressive membrane action and fixed boundary action as well as the effect of lateral confinement.

This thesis explores a suitable method and appropriate input to determine the failure probability of thermal shrinkage cracking in a steel fibre-reinforced underwater concrete floor by examining the factors that influence this failure probability.

An underwater concrete (UWC) floor is a common construction type in the Netherlands that is often applied to create building pits under the groundwater table. Usually, these (generally unreinforced) UWC floors only function as a watertight bottom layer of the building pit with only a temporary sealing function. Water tightness and crack prevention are very important aspects of this type of construction. A permanent reinforced structural top floor is frequently used on top of the temporary UWC floor to make a completely watertight construction, which is not the most sustainable and cost-efficient solution. Advances in concrete technology such as fibre-reinforced concrete have made it possible to integrate both the UWC and structural top floor or even use the UWC floor as the permanent structural floor. In these cases, the UWC floor should already function as a watertight barrier and controlling leakage by limiting the crack width becomes even more important. The addition of fibres to concrete may prevent through crack formation in the UWC slab and the possible consequent leakage. An important cause of cracking in UWC floors is thermal shrinkage during the cooling phase of the hardening reaction shortly after casting the UWC floor.

Currently, there are no guidelines for the construction of fibre-reinforced concrete (FRC) floors and the prevention or limitation of thermal shrinkage cracking. A CROW-committee "Steel fibre reinforced underwater concrete (SFRUWC) floor as permanent structural floor" has been formed. This committee aims to set up a design recommendation and part of that is addressing the thermal shrinkage cracking problem. There is a lot of uncertainty in geometry, material properties and boundary conditions associated with SFRUWC floor design and construction. Because of this, there is a need for a probabilistic approach to investigate the influence of these uncertainties and tolerances on crack formation in SFRUWC floors during the hardening phase. This research aims to determine a suitable probabilistic method to investigate the failure probability of SFRUWC floors and the parameters that influence this.

In order to achieve this, a finite element model was developed that determines the shrinkage cracking behaviour in a part of a UWC floor in a building pit. Before this model could be developed, all the necessary input parameters and design equations were collected from literature and existing guidelines. To set up a model, first the behaviour of UWC floors was studied, followed by the development of a finite element model that includes the hardening behaviour and strength development of young concrete. An important aspect of this finite element model is the use of random fields to introduce spatial variation in the strength properties of the SFRUWC floor, which is a first step to include stochastic variation in the model for the probabilistic analysis. A probabilistic sensitivity study was performed with the finite element model by calculating multiple samples for each set of input parameters. Separate input parameters were varied and the influence on the results was investigated. The parameters that were considered, include the random field properties, material properties and thermal properties. Finally, a full Monte Carlo analysis was performed to give a proof of concept on how to calculate the failure probability regarding thermal shrinkage cracking in SFRUWC floors.

In order to prevent leaking cracks and satisfy the crack width criterion, the tension-hardening behaviour of FRC has to be utilised. Tension hardening behaviour will lead to a distributed cracking pattern, consisting of multiple small cracks which can satisfy the crack width criterion as opposed to a single large separation crack which does not satisfy the maximum allowable crack width criterion. It was found that the tensile behaviour of FRC and the use of random fields to model this tensile behaviour were major parameters that influenced the crack width and the occurrence of a distributed crack pattern. An important parameter is the standard deviation of the random field, which influences the difference between the maximum and minimum tensile strength in different locations in the slab. Looking at material behaviour, the main conclusion was that the introduction of a small hardening branch in the tensile material model was the governing influence factor. Both the standard deviation of the random field and the introduction of a hardening branch in the tensile behaviour affect the ratio between the tensile strength of the ordinary concrete and the residual tensile strength of the fibre-reinforced concrete. These two factors in combination with the model that was used, turned out to be dominating the results in such a way that the other input parameters only had a relatively small influence on the crack widths.

To determine maximum crack widths in SFRUWC floor it is essential to consider multiple samples with different random fields to find out if only a distributed crack pattern is possible or whether also single localised cracks can occur. The possibility of both these results being able to occur, leads to a large possible error in the maximum crack width. The results of this thesis have shown that the random field parameters remain uncertain and experimental research is needed to determine these correctly. Until then, it is important to investigate how significantly these parameters influence the results. It is recommended to extend this research by improving the model by making it more realistic and finding out if these two factors are still the dominating input parameters.

Port of Rotterdam has the ambition to reduce the footprint for building new quay walls, this is in line with their ambition to reduce the footprint and with national goals to limit global warming. The aim is to use less materials and/or use different design solutions. These reinforced structures are designed in a conventional way and the internal forces are determined by performing a Linear Elastic Analysis. The reinforcement is calculated using the internal forces and is based on the Eurocode 1992 -1-1. The conventional approach includes various assumptions that affect the amount of concrete and steel used, which influences the CO2 footprint, structure reliability, and costs. In order to know the effects of these assumptions, advanced nonlinear calculations are carried out using volume elements

In the construction of subsoil structures, a common challenge is the presence of a high groundwater level in combination with the absence of a naturally impermeable layer or an environment susceptible to settlements due to lowering the groundwater level. To overcome this issue, a building pit with an underwater concrete floor (UCF) can be constructed. The UCF ensures structural rigidity and allows for the building pit to be drained such that a dry and safe subsoil construction site is obtained.

The objective of this thesis is to investigate how design efficiency of underwater concrete floors can be improved. In an effort to reduce material usage and achieve cost-effective structures, the following research question was stated:

“What is the influence of design parameters and how can parameters be adjusted to improve design efficiency of an underwater concrete floor, and to what extent can the addition of fibre reinforcement contribute to this optimization?”

A parametric model was developed to provide insight to the sensitivity of parameters and their impact on design resistance. Furthermore, the model was utilized to examine under what circumstances potential material savings can be obtained by implementing fibre reinforced concrete in UCF’s. This was accomplished through the evaluation and comparison of the minimum required thickness based on bending moment resistance in various scenarios, for both UCF’s and steel fibre reinforced UCF’s (SFUCF).

Results obtained with the parametric model established that, in order to enhance the bending moment resistance of an uncracked UCF, increasing the nominal thickness becomes relatively more effective compared to increasing the concrete strength class for higher normal forces. When utilizing a compression arch to obtain bending moment resistance, the implementation of ribbed tensile elements or an increase in nominal thickness are found to be the most suitable methods for increasing resistance. For enhanced shear force resistance, increasing the nominal thickness over the concrete class provides relatively more additional resistance for slender UCF’s. The results found that through the application of ribbed piles, most punching shear force resistance can be obtained.

Three use cases for a SFUCF were identified using the parametric model. When centre to centre (c.t.c.) distances larger than 4.4m are applied in combination with a substantial normal force, significant material savings of up to 0.3m thickness are possible, which equates to a reduction of material usage by 30%. For situations where the effective height of the compression arch is small, it was also found that material usage could be reduced by 30%. Perhaps the most significant use case for a SFUCF is when the normal force is close to zero, and additional normal force cannot be obtained through membrane action. In these situations, the application of a SFUCF can make an otherwise near impossible project feasible.

As a new design approach, a cost-based optimization tool was developed using the parametric model. An already executed UCF was evaluated using the tool, it was determined that a more cost-effective design could have been achieved, with potential savings of up to 30% in costs.

A significant part of composite concrete viaducts was built in the 50s and 60s. This has led to an increasing need for the reassessment of the precast concrete beam bridges in the Netherlands. Many of those bridges are nowadays subjected to higher traffic loads and consequently, have a certain risk of not complying with the currently used design codes. As a result, there is a demand for the development of nonlinear finite element solution strategies, which would increase the reliability of the numerical methods in safety assessment. In this research, special consideration is given to the precast, prestressed beam bridges which were made continuous by applying cast-in-situ cross beams and a top layer above the supports. In such structures, the hogging bending moment introduces more complex stress conditions in the concrete parts and more specific at the interface between precast girders and the top slab, compared to simply supported beam bridges.
Thus, one of the key aspects of the structural performance of composite bridges is the interfacial behaviour. The focus of this research is to study the stress conditions in the vicinity and at the interface and explore methods of numerical modelling of the interface in concrete-to-concrete connections between precast beams and top layers to initiate the development of modelling strategies for this type of interfaces.
The literature review was focused on prefabricated beam bridges, the current state of knowledge on concrete-to-concrete interfaces, along with design recommendations and past experimental and numerical research. Moreover, available interface element types, material models and modelling guidelines were explored. Since DIANA FEA is used within the course of this research, the study of the available models was limited to the ones provided by this software. It was noted that the Linear Elasticity model is the simplest way of interface modelling, therefore it was utilised in the initial stage of the research. More advanced models, Coulomb Friction and Combined Cracking-Shearing-Crushing, were considered worth investigating owing to accounting for coupling between normal and tangential behaviour. The Nonlinear Elasticity material model was also recognized due to the introduction of nonlinear effects, yet being relatively simple to assemble.
The initial phase of the research was a linear, phased analysis of the continuous, composite, concrete girder. Three models were tested within this part of the research – the model without interface elements, and two with linear elastic interface elements, one having high, penalty stiffness and the other having lower, more realistic value of shear stiffness. It was verified that the models without and with penalty stiffness interface performed almost equally. The decrease in stiffness and the deterioration of the composite action caused by this, resulted in an increase of stresses in the precast element. By the support, the extreme tension raised by a factor of 1.21 and under the point of load application the compressive stresses in the beams’ web elevated by 2.26. Based on the linear analysis, no significant tensile stresses perpendicular to the interface were detected. According to the analysis of interfacial stresses interaction and assumed failure envelopes, at four chosen points - above the support, at midspan of the main span, at the local shear extreme and under the point of load application - it was observed that the point above the support is not at risk of failure, whereas the point in the midspan might be. It was concluded that the combination of stresses is relevant not only because of a possible decrease in capacity due to tension but also increase under compression. As a result, models accounting for coupling between normal and shear tractions and relative displacements are worth investigating. It was also observed, that cracking in concrete elements by the support is expected, hence nonlinear analysis is required.
The component-level experiments found in the literature were analysed in the following section to be able to perform verification study of Coulomb Friction (CF) and Combined Cracking-Shearing-Crushing (CCSC) interface material models. Based on single element FE tests it was concluded that both material models proved to be well-suited for capturing the shear-normal stresses coupling. With the same input parameters, but higher normal pressure, the shear capacity increased, representing well the reference data. The CCSC interface material model’s ability to capture both cohesion and friction softening, was also verified with the single element models. Moreover, tension softening based on mode I fracture energy can be accounted for in that material model, as well as the fracture energy’s and dilatancy’s dependency on confining stress. However, those parameters were not verified, due to, among others, limited experimental data. Element assembly with the CCSC material model for the interface, circular beam bond-slip reinforcement and nonlinear material properties of concrete, was used to analyse the specimens with rebars crossing the interface. This approach, was assumed to represent the force transfer mechanisms to the highest extent, since cohesion and friction, generated by both external pressure and reinforcing bars, along with their softening, as well as dowel action, can theoretically be represented by such model. It was observed that this type of strategy resulted in convergence issues, and due to large number of input parameters it is quite complex to analyse or further calibrate. However, the approach seemed promising since the peak loads were underestimated by only 7-15% with respect to the mean, experimentally obtained values.
In the final Chapter the Combined Cracking-Shearing-Crushing (CCSC) interface material model, with bond-slip beam reinforcements was applied in the nonlinear analysis of the previously analysed composite girder. As an alternative, the model with the Nonlinear Elasticity(NE) interface material model was also constructed, based on the analogous input parameters, to be able to compare the modelling methods. In total four models were analysed, since two sets of input, one based on Eurocode 2 and the other on best guess stemming from literature findings, were studied. What was found to be promising is that the global behaviour, assessed on the basis of crack patterns, of the beams with corresponding input, was quite similar for the analyses with the CCSC and the NE material models. With the applied numerical setup, it was not possible to obtain the total load-displacement path of the composite beams using the CCSC material model for the interface, since the models diverged. The NE material model performed more stable and allowed for the analyses to continue, which is its main advantage. Another benefit is the ease of assembly, in comparison with the CCSC model. Nevertheless, it was demonstrated that the NE might provide overestimated results due to not considering the interaction of tractions. It was highlighted that the models’ validation with experiments is needed to recommend one of the models or either of the input sets. It was recommended to simplify the approach with the CCSC material model, by for instance, simplifying the numerical setup of interface reinforcement. Moreover, according to the literature findings the scatter of cohesion and friction coefficients, as well as other input parameters, is still quite large, thus experimental research in the form of push-off tests focused on those, particular interfaces is recommended.

In the energy sector, a transition is made from fossil fuels to sustainable energies. Due to an irregular supply of these sustainable energies, it often occurs that there is a mismatch between supply and demand. Energy storage is a promising technique to overcome this. In this thesis, the aim is to store gravitational energy in concrete spheres which are placed on the seabed.

Therefore, this thesis aims to answer whether the most optimal construction method uses 3D Concrete Printing (3DCP) and if so, what the optimal construction method will be using 3DCP. Based on a specific case, five main construction methods are qualitative investigated, from which two are with 3DCP. From an evaluation, it followed that a combination of 3DCP and conventional casting is the most promising method and is therefore selected for more in-depth research. In this construction method, the formwork is made with 3DCP and concrete is cast in the formwork. A prefab bottom and top part are required, because the maximum inclination (nowadays) for printing is limited to 45°.

Based on the selected construction method, three different 3DCP-variants are investigated: construction in the dry (1), submerged construction (2) and construction on a pontoon (3). The two main topics that are investigated are the use of 3DCP for the formwork and the suitability of unreinforced concrete for the sphere itself. The possible use of 3DCP is verified based on two failure mechanisms: plastic collapse (results in minimal free height of the formwork) and elastic collapse (results in maximum free height of the formwork). The suitability of unreinforced concrete is verified based on strength requirements.

Both in case of construction in the dry and construction on a pontoon, h1 is 0.20 m and h2 is 0.65 m. In case of submerged construction, h1 is 0.25 m and h2 is 0.72 m. The unreinforced wall thickness should not exceed 2.5 m because it is required that the sphere is buoyant. For this wall thickness, a concrete strength class of C60/75 is required for construction in the dry, submerged construction and construction on a pontoon. An evaluation based on feasibility and reliability, combined with the results above, shows that construction in the dry is the most promising method.

An adiabatic calculation is made of the temperature increase of the concrete, based on five different cement compositions. It followed that unreinforced concrete will crack. However, in reality, the temperature increase is semi-adiabatic, resulting in lower tensile stresses. It is therefore highly recommended to further investigate this temperature increase in order to verify the suitability of unreinforced concrete. Measures that could be taken to lower the temperature differences are: addition of liquid nitrogen or addition of ice instead of water for the concrete mix. Besides that, it is recommended to investigate the possible use of fibre-reinforced concrete, which could significantly increase the tensile strength of concrete.

Nowadays, Rijkswaterstaat reassesses many older concrete bridges to guarantee their structural safety under the influence of increased traffic loads and stricter standards. Many of these concrete bridges contain open straight-legged stirrups, which are not allowed to take into account for the calculations of the shear resistance according to current standards. This often results in theoretical insufficient shear capacity and critical damage to structures, but this is not observed in reality. This indicates that the open straight-legged stirrups probably do contribute to the shear resistance, where an accurate assessment of this contribution could prevent unnecessary and costly structural safety measures. However, very few shear tests with relevant cross-sectional dimensions are performed and documented in literature, especially tests containing open straight-legged stirrups.

The application of Nonlinear Finite Element Analysis (NLFEA) is a useful tool to evaluate and understand the behaviour of structures, but provisions for the implementation of open straight-legged stirrups in concrete structures are lacking. Thus, the goal of this research is to provide a finite element modelling strategy that is able to accurately describe the behaviour of concrete beams with open straight-legged stirrups subjected to shear. The research focusses on describing the behaviour of rectangular concrete beams with open and closed straight-legged stirrups with finite element models using DIANA 10.5 [1].

Schramm [2] has performed multiple shear tests on prestressed concrete beams with several no longer permitted stirrups, including open straight-legged stirrups. He found that open straight-legged stirrups can significantly contribute to the transfer of shear forces [2]. The relevance of the rectangular test beams for comparison with box-girders is validated in this thesis, where the stress distributions in a linear elastic rectangular and box-girder cross-section due to axial forces, bending moments, shear forces and torsion are compared.

In the interest of providing a suitable solution strategy, Schramm’s test beams with closed and open straight-legged stirrups are reproduced with 3-dimensional nonlinear finite element models based on the recommendations of the RTD1016-1 [3], where the influence of various modelling considerations is investigated. The concrete is modelled with a smeared total strain-based crack model with the Hordijk tensioning and parabolic compression relations, including confinement and lateral cracking effects. Reinforcements are modelled as embedded truss elements with the Von-Mises plasticity model. To describe the accurate anchorage behaviour of the open straight-legged stirrups, the interaction between the surrounding concrete and the stirrups is described with the Shima bond-slip relation. The finite element model is first calibrated with a beam with closed stirrups, where modelling clamped restraints with supports on both sides of the beam result in a too-stiff response. By allowing a little rotational freedom in the form of boundary springs, the stiffness of the beam is manipulated without changing the overall load-bearing behaviour...

The light and frequent earthquakes in the north of the Netherlands, particularly in the province of Groningen, have recently exposed the unreinforced masonry structures to seismic activities. Since these structures do not adhere to seismic regulations, they are considered vulnerable to seismicity. The ultimate state capacity of the structures is important for an individual's safety, however, these earthquakes are of low intensity and cause aesthetic damage.

In order to investigate the light damage initiation and development, TNO has performed shaking table tests on an unreinforced masonry (URM) cavity wall specimen in out-of-plane (OOP) one-way bending with small increments in intensity. The test specimen consisted of calcium silicate brick inner leaf and perforated clay brick outer leaf. The damage development in the outer leaf was monitored during these tests using a high-speed digital image correlation (DIC) technique to study the initiation and development of damage in the outer leaf of the specimen. The experimental tests showed damage initiation at the mid-height of the outer leaf. The tests could not capture the development of cracks through the thickness of the cavity wall.

The scope of this research is a numerical assessment of the experimental study by using a Non-Linear Time History (NLTH) analysis of light damage initiation and development of a URM cavity wall under out-of-plane loading. The high-resolution experimental results are used as a basis for the development and calibration of models which can better predict the crack initiation and development in URM. The finite element software DIANA 10.5 FEA was used to set up the numerical model and conduct transient analysis.

The seismic signal as an input loading and the top boundary condition of the test specimen. The acceleration data measured from the shaking table tests at the base was used as an input seismic signal for the transient analysis of the models. The input signal needed to be processed before application as the presence of low-frequency content leaded to inaccurate results. Different approaches are discussed in this thesis regarding the processing of the input acceleration signal.

The experimental tests were modeled along the cross-section of the test specimen, thereby highlighting the thickness of the inner leaf and the outer leaf. This enabled tracking the light damage initiation and propagation through the thickness of the cavity wall. A total of thirteen shaking table tests were conducted on the experimental setup. In order to gain insight into the behavior of the specimen during each shaking table test, a model was created corresponding to each shaking table test. Preliminary analysis schemes were set in order to check the validity of all thirteen models. The two cases of top boundary conditions were checked, roller support and spring-mass support. The roller boundary condition proved to be stiff in comparison to the experimental results.

The numerical results were calibrated on the basis of material properties. The results were compared to experimental results by checking the dynamic behavior at the mid-height, dynamic behavior over the height, and light damage initiation and development of the specimen. The results of the numerical models were stiff in comparison to the experimental results. According to the conclusions, it is recommended to research further regarding the boundary conditions, especially the bottom boundary condition due to the formation of a rocking crack. Another important aspect to focus on is the combination of all input signals, thereby, taking into consideration the damage accumulation.

The construction sector plays a significant role in the environment, and concrete structures constitute a substantial portion of this sector. The government is actively seeking ways to reduce the environmental impact of construction activities by promoting a more sustainable approach. In the Netherlands, a considerable number of repetitive cellular residential buildings are constructed using the tunnel formwork building method. Although this method can be enhanced in terms of sustainability by utilizing environmentally friendly cement mixtures, it poses challenges, such as an increase in execution time. This research aims to explore a more sustainable approach to the tunnel formwork building method while devising strategies to maintain the same execution time as before.

The tunnel formwork building method operates with a 24-hour daily execution cycle. During the initial 8 hours, the formwork, reinforcement, and installations are set up, followed by pouring concrete at the end of the day. After 16 hours, the concrete attains sufficient strength for the formwork to be dismantled, allowing it to be placed on the next grid. This approach results in rapid construction, high-quality output, and cost-effectiveness. However, a significant drawback is the reliance on CEM I mixtures, which consist of approximately 100\% Portland cement, contributing to substantial greenhouse gas emissions and environmental impact. Blended cement mixtures, such as CEM II and CEM III, offer more environmentally friendly alternatives by incorporating lower percentages of Portland cement blended with fly ash or blast furnace slag. Despite their environmental benefits, these mixtures exhibit a slower strength development, making it challenging to achieve a hardening time of 16 hours.

In pursuit of a dependable and sustainable approach to the tunnel formwork building method that preserves the 24-hour daily cycle, the research question is articulated as follows: "What concrete mixtures and execution strategies can be applied in the Netherlands to diminish the environmental impact of the traditional tunnel formwork building method, utilizing sustainable cement mixtures, while upholding existing advantages in time, cost, and quality?" This research question will guide the exploration of optimal concrete mixtures and execution measures for implementing sustainable cement mixtures within the tunnel formwork building method, while ensuring the continuity of the daily execution cycle.

In addressing this research question, an Excel calculation sheet has been developed. This sheet serves to compute the material costs, shadow costs, and formwork removal time associated with specific modifications in the design, concrete mixture, and additional execution measures for the tunnel formwork building method. The calculation sheet offers flexibility with three grid sizes: 4.5m, 6.0m, and 7.2m. It incorporates various concrete properties, such as the cement mixture (CEM I, CEM II, or CEM III), w/c ratio (0.45 or 0.55), aggregate types (fine and coarse), Blaine value (300 or 400$m^2/kg$), and admixtures (basic and additional). Additionally, the calculation sheet allows for adjustments in seasonal conditions, with options for summer (20°C) or winter (10°C)...

The Netherlands is currently facing a significant challenge regarding its highway system due to the rise in traffic, especially in densely populated areas like The Randstad. However, constructing new infrastructure or replacing old bridges is not a practical solution due to environmental concerns. Most of the country's prestressed concrete bridges were built in the 1960s and 1970s with a lifespan of 100 years, and they are deemed incapable of handling the current traffic volume. As the existing bridges are still in good condition, recent projects have focused on widening them. Widening a bridge involves careful consideration of the behavior of all the elements in relation to each other, given the existing deck's relative stability and the inevitable shrinkage and creep of new components. To ensure a monolithic connection between the new and existing sections of the bridge, current projects aim to widen the bridges using a closure pour between the main slabs.

The Schipholbrug, situated close to the Schiphol Airport, is a prime example of a prestressed bridge that needs to be widened, and it is the focus of this thesis. In the Netherlands, reinforced concrete is the preferred material for a closure pour due to its durability, cost-effectiveness, and established properties. However, to maintain the integration between new and old concrete, a 6-9 month delay after constructing the new bridge is necessary to build this closure pour. To minimize significant delays, it is crucial to maintain a strong connection between the original and new materials, including the closure pour. The main challenge is managing the differences in creep and shrinkage between the existing structures, fresh deck, and closure pour. These inconsistencies can cause significant tensile stresses in the closure pour, especially when delays are kept to a minimum. Therefore, identifying a cementitious material that could effortlessly create reliable bonds with the primary decks' prestressed concrete and possess a high tensile strain range property was necessary to reduce this delay.

Strain-Hardening Cementitious Composite, also known as SHCC, is a modern material that possesses an impressive tensile strain range and a comparatively lower elastic modulus. Nevertheless, what sets it apart is its strain-hardening quality, which improves its toughness even after experiencing cracks. This exceptional characteristic of SHCC allows it to offer an extended tensile strain range, making it a choice for a closure pour.

The thorough literature review investigated crucial subjects, such as the intricacies of closure pour when expanding current bridges. Moreover, it covered the fundamental attributes of concrete that are pertinent to this thesis, such as shrinkage and creep, as well as its post-crack behavior. Another segment focused on the primary material employed in this thesis, SHCC, emphasizing its fundamental characteristics, including shrinkage and crack. Lastly, the research included a section on imposed deformation that was custom-made to the specific case of this thesis.

The methodology chapter utilized analytical calculations to gain a better understanding of the deformation issues caused by shrinkage and creep and their effect on the closure pour. These calculations explored composite structure mechanics and imposed deformation to determine the longitudinal stresses present in the mid-span of the decks. To further verify the accuracy of the findings, a linear model was also developed using DIANA FEA...

The thixotropic properties of contemporary mortars allow the insertion of mortar in small vertical seams by using a mortar pump without the need for traditional formwork. In such a seam, a vertical mortar connection for the transfer of shear forces can be created by simply adding a profile to the mortar-to-concrete interfaces. In this way a constructible continious vertical shear connection can be constructed between storey-high precast concrete wall elements. In this investigation, narrow vertical mortar connections are developed for the transfer of shear forces in precast concrete shear walls with tying reinforcement in the slabs. The shear behaviour of five versions with differently shaped mortar-to-concrete interfaces is obtained from shear tests. All experimental results are presented and discussed, while the shear behaviour of the Staggered shear key connection is analysed in detail. Also, the shear behaviour of the five mortar connections are mutually compared and assessed on their performance for functioning as a vertical mortar connection. A diagonal bar model is proposed for simulating the shear behaviour of the Staggered shear key connection, which is called the “inclined compression strut model”. Also, an equation for predicting the shear capacity is proposed. The functioning of the model and equation are investigated by applying them in case studies with cantilever shear walls in versions with and without window openings.@en

A series of critical transmission lattice towers failures due to severe ice and wind loads forced German utility companies to reassess the structural stability of their power grid infrastructure. During the structural reassessment process, a problem related to an outdated or even missing documentation of the in-use infrastructure occurred. This issue forced utility companies to gather the data regarding the geometry of the lattice towers on-site, using specialized and labor-intensive geodetic measuring methods. The scale of the required data acquisition endeavor and stability checks to be performed encouraged the use of alternative methods to capture the geometry of the in-situ structures and reconstruct geometric models to be applied during the structural stability checks in a reliable and efficient way.

This work presents an innovative method to generate a geometric CAD model using point cloud data captured by a LiDAR scanner. The CAD model can be later implemented for FEA utilized during structural stability assessments. The modeling process defined in this study is fully automatized, enabling to obtain repeatable results and save the time required for manual data processing. For the input point cloud data, two types: Aerial and Terrestrial LiDAR point clouds have been investigated allowing to identify the applicability of both data sets for the proposed method.

The model generated with the automatic method proposed in this study is compared in terms of geo-metric discrepancies to an idealized model based on design documentation and a LiDAR point cloud based model manually generated with a commercial software. The two models used for comparison depict a traditional structural engineering approach and a state-of-the-art method within the point cloud processing field accordingly. At the final stage of this work, the automatically generated point cloud based model is used for a non-linear FEA and compared to a FEA response of the idealized mod-el.

Results showcase that LiDAR point cloud data is a good source of geometric information to reconstruct a geometric CAD model which can later be implemented in FEA. Obtained results are comparable to the ones of an idealized model based on design documentation in terms of collapse mechanism and ultimate load applied at the failure step. Additionally, the geometrical comparison between the point cloud based models generated with the manual method and the one proposed in this work underline the ad-vantage of the automatic method in terms of permissible level of detail and overall precision of the final geometric model. What is more, the impact of point cloud data usage for FEA modeling is shown. Investigating differences between FEA results of the point cloud based and idealized models allow to showcase the influence of real life imperfections on force redistribution across the analyzed structure and ultimate forces reached by members loaded in compression.

The modeling method and analysis results presented in this work can be applied as a set of guidelines for future applications related to point cloud data processing of steel lattice structures used for FEA modeling purposes.

In this thesis an investigation into the buckling behaviour of steel trusses with eccentric joints is performed.
In recent years, Ampelmann motion compensated gangway systems have been pivotal to the advancement of offshore personnel transfers. These systems for functionality reasons require the use of eccentric joints. The behaviour of such joints is not a well-studied topic, and little is known of their effect on the buckling behaviour of structures. Buckling of trusses using conventional centric (non-eccentric) joints has been examined extensively in the literature. This work aims to answer what the effects of using eccentric joints compared to centric are, on the stability of steel truss structures. Additionally, a reduction of the computational and design time is attempted, by extending a simplified approach developed for centric joints, to eccentric joints.
The main investigation is performed on a simply supported truss comprised from eccentric K-joints and square hollow sections (SHS). Detailed models are used, with the joints being modelled by shell elements. The results are compared to equivalent trusses with centric joints. The main conclusions are that due to the eccentric joints, a better buckling behaviour can be realised for the truss members in the case of in-plane buckling. This improvement is more evident for the buckling of the braces and for combinations of chords and braces with γ>8 and 0.30<β<0.70 respectively. In those cases, a decrease of the buckling length of at least 5% is observed and reaching nearly 20% for γ=15.9 and β=0.4. In the case of out of plane buckling, the observed behaviour is slightly worse. The difference is considered negligible in practice, with all configurations checked giving a difference of less than 2% between the buckling lengths.
The simplified design approach, which uses beam elements and rotational springs, is validated, by comparing literature results with detailed shell element models. It is, also, further improved by performing new research on individual centric K-joint models. Having validated the approach for centric joints, three different modifications are proposed to extend it to eccentric joints. None of the proposed modifications give the validation required but insight is gained regarding the behaviour of eccentric K-joint trusses. It is concluded that eccentric joints require non-symmetric stiffness matrices for their behaviour to be captured.

Climate change is changing the world. Where previously efficient use of materials was mainly applied to realize cost savings, this can also help to reduce the footprint of a construction. There is a rather direct and obvious relationship between the amount of material required in a construction and its environmental impact. Of course, the environmental impact is not solely dependent on this metric, but minimizing the weight of the structure is a great starting point. This thesis focusses on minimizing the environmental impact of a welded truss bridge. In addition to the required volume of construction material, the environmental costs for the welding and conservation are also taken into account. A case study is performed on a bicycle bridge crossing a highway that is built in the Netherlands.

The thesis starts with a review of multiple methods that minimize the weight of a structure. Within the field of structural optimization, The Ground Structure Method (GSM) appears to be the most suitable method for large structures that consist of slender structural elements. Making utterly high refinements in the GSM-model will result in a structure with definitely the lowest volume possible. However, this structure will have lots of smaller and shorter elements that will require in total more welding and conservation. This will not lead to a least-environmental-impacting structure. Thus the main question arises:

Will, within the ground structure method, minimizing on the environmental impact result in a significantly different structure than a minimization on weight?

The objective function for the environmental impact consists of the three considered contributing factors: the construction material, welding and the conservation. The environmental impact for the three factors is determined with a Life Cycle Assessment (LCA). Finally, every contributing factor is unified into a single indicator value through the Environmental Cost Indicator (ECI) method.
The objective function also consists of three variables which represent: the volume of construction material, the welding volume and the surface of the structure. The volume is already known, since it is the regular GSM minimization. The welding volume can be determined through the joint-cost method, which is adding an artificial length to each member. The surface area of the structure is harder to determine. The relation of the volume of a construction element and its surface area is generally speaking non-linear. Multiple implementations were investigated. The aim is to perform the optimization on a fully connected ground structure, and so the assumption is made to make the relation between the volume and surface area linear. A circular hollow cross section with a variable radius and a constant wall thickness is implemented into the optimization method. The final objective function to minimize the ECI costs is a mixed-integer linear programming problem (MILP).

This method is tested on the established benchmark for a cantilever structure and on a case study for a bicycle bridge. The shape of the optimal structure is dependent on the amount of nodes within the design domain. The results for the cantilever structure does clearly reflect this. Depending on the amount of nodes in the design domain, the minimization of the environmental impact is decreased between 0 and 37%, while the weight is at most 2.5% higher. The difference of the environmental impact between the least-weight and least-environmental-impacting structure keeps increasing as the node density increases.
The bicycle bridge is optimized in a 2D and 3D design domain. The design domain of the bicycle bridge appeared to be too big to be solved by the MILP formulation optimization, thus the domain is reduced to a single span of the bridge. Furthermore, the amount of nodes in the design domain is limited to improve the computability of the problem. In both the 2D and 3D variant the regular minimization on weight requires only a fraction of the time to solve the problem successfully. For the 2D case there is a difference between the minimization of the weight and ECI. The number of members in the least-environmental-impacting structure is reduced by 40%, which results in a 1% lower environmental impact. The MILP could not converge properly in 4 hours in the 3D design domain. This is mainly because the model size did increase a lot compared to the 2D design domain. Going from 2D to 3D adds a third axis, which increases the amount of constraints by 50%. Likewise, the number of nodes in a 3D domain increase more rapidly than in a 2D domain.

All in all, the method is implemented successfully and validated with the cantilever structure. The proposed method will result in a structure with an equal or lower environmental impact compared to the regular least-weight minimization. However the minimization of the environmental cost with the proposed optimization method is able to solve problems with around 5,000 variables. To solve larger models successfully it is advised to either reduce the connectivity of the ground structure or to apply the joint-cost method with an LP.

With the rising demand for renewable energy sources the amount of wind turbines which are built on land are growing rapidly. Because of the repetitive nature of the foundation small design improvements can add up to large savings in material usage and building cost. The most critical part of the foundation is the connection between the metal mast and the concrete foundation. This connection is made by implementing an anchor cage. The application of an anchor cage results in complex multiaxial stresses in the surrounding area. Confinement plays a large role in the compressive strength of the concrete subjected to the partially loaded area created by the anchor flange. The main goal of this thesis is investigating the best way of modelling the concrete surrounding the anchor cage at confinement levels being present in the wind turbine foundation. This is done by investigating the theory regarding confinement and the effects of it. But also the way this is captured by analytical models. To make a comparison between DIANA and the analytical models the present stress situation in the wind turbine foundation is analysed. Looking at the stress distribution and the confinement levels. Next a comparison of the ideal case of confinement is made. This is later expanded to a larger scale model, to compare the effects of confinement. The confinement present will enhance the concrete strength and strain properties. The concrete specimen can resist larger loads and reacts more ductile. These properties are captured in analytical confinement models, these are compared to the way DIANA approaches confinement. The anchor rods between the anchor flanges are prestressed, this prestressing results in a permanent stress situation. Within this stress situation there is a small part beneath the anchor flange subjected to confinement. With increasing pressure, originating from the moment load which results from the wind on the tower and it’s blades, the confined area increases to the top half of the foundation. With significant confinement in the pedestal. Comparing the DIANA compressive behaviour models with the analytical confinement models and experimental data within a one element model. It is seen that compressive behaviour models do react on the confinement. Although they show a lower peak strength than the analytical models. A larger difference is noted in the underestimation of the peak strain. This difference in outcomes is the result of the different approaches between DIANA and the analytical models. As well as some assumptions that DIANA makes concerning the strength and strain increase factor. The Parabolic compressive curve is most suitable for modelling the confinement in this ideal case. A case study is conducted to further investigate how the confinement is represented in a total non-linear model. Modelling the top part of the foundation and checking the effect that confinement has on this model. For this model the prestressing of the anchor rods is increased until failure. Without confinement the concrete elements directly beneath the anchor flange fail in compression. Running the model with confinement it is noticed that the underlying weaker concrete is failing in compression first. This is the result of the confinement being present surrounding the anchor flange. The model with confinement is also able to resist a 30% larger load than the model without confinement. The parabolic compression curve is the most suitable curve currently available inside the strain based crack model for modelling the effects of confinement. Overall DIANA is able to capture the effects of confinement well enough to see the positive effects in the case study. Due to limitations in the analyses performed and in their interpretations, it is not possible to give an unequivocal answer on the effect of confinement within the foundation of the wind turbine.